The general areas of pulmonary host defense and nosocomial infection are being investigated, using Pseudomonas aeruginosa infection as the prototype because of its frequent occurrence in immunosuppressed patients. Nosocomial infection is being studied in immunosuppressed animals with emphasis on protection against death by active immunization with a type-specific lipopolysaccharide antigen and a "cross-protective" core antigen, OEP. In paticular the efficacy of these vaccines in reducing the quantitative requirements for granulocytes to protect against death in neutropenic hosts is being investigated.